I'm tutoring an adult student who is pretty advanced. Her problem is that she can write well, but when it comes to speaking, she uses incorrect grammar especially in the area of verb tenses. She mixes up her verb tenses when speaking. What are some things I can do to improve her speaking accuracy especially with verb tenses?

Tape her talk and then type it out so she can see the things she is doing. She can correct the written words herself and that will make her more aware of what she is doing. It probably won't help for a while though. These things take time to come to awareness.

You can also just have her say a sentence at a time and you can say it correctly, as quickly as you can after her. It makes for a stilted conversation and she will probably stop talking after awhile. I usually do it for three or four sentences and then stop so that she can communicate what she wants to communicate or she will get frustrated.

The taping usually words the best. Of course if you have a computer that records and then writes conversations, you have it made. It only takes a few times for the computer to start to understand her words and she can see them being printed as she says them which is also great for spelling. You can then let her go over the whole conversation and pick out her errors. I probably wouldn't point out ones she missed as it will be enough to deal with the ones she does catch but you both will notice a pattern after awhile.

You could also take a look at (lists of) particularly frequent verbs, and start practising them in present and past contexts; it might be good to start with irregulars, as they often sound particularly different. Quality learner dictionaries such as those from Longman, Oxford, COBUILD, Macmillan, and Merriam-Webster can all be helpful in this regard (and most have free online versions); then, there are online corpora such as the BNC that you can search for tagged strings (very useful with regard to compound tenses; instructions and link here: http://forums.eslcafe.com/teacher/viewtopic.php?p=41753#41753 ), and the following may be very useful too (basically a lexicogrammatical/structuro-semantic organization of verbs; verbs that share similar structures often have quite closely-related meanings): https://arts-ccr-002.bham.ac.uk/ccr/patgram/ .

Bear in mind that there is sometimes a slight difference in function/meaning/usage between present and past tense (but this can be more helpful than not):

I see (what you're saying). (="can understand, appreciate")

I saw Tom the other day. ... (the literal, visual-perception meaning of the verb)